Time machine is backing up twice to my external hard drive

I thought I'd seen just about all there was to see with TimeMachine...you've proven me wrong. The thing is, the way TimeMachine performs its magic, I just wouldn't trust this current backup going forward. You could remove the Natalie backup drive(s) and then re-establish just one but what has happened in the meantime? As backups get 'folded' into each other what is TimeMachine doing with these apparent duplicates? what kind of havoc (if any) is this creating?

If there might be items on the backup that you think you need to keep then purchasing a new drive for backups going forward really is the safest thing to do. If not, erase the backup and start over. If this were a standard with an archival system I'd be more willing to talk about a solution that fixes the issue going forward but with TM, no.

If the external device was dropping out intermittently due to power problems, there may well be a latent corruption, and the easiest approach is to wipe and start a new Time Machine backup. The other possibility is two Time Machine backups on the same disk, though I’ve not previously met similarly-named co-resident archives. If you want to keep the backup, I’d get and use a different disk and use that until this backup ages out. It’s possible to archive the old backup, once you get the new one going, and migration (very slow) is also possible. But I’d shelve this for a few months, and then re-format and re-use the existing and old and possibly corrupt Time Machine disk.

I would prefer that, too. But this TM config looks sketchy, who knows what else is corrupted due to the drop-outs, and whether that disk is “merely” oddly corrupt for failing, I’d prefer a good backup. TM copies take approximately forever, too. Starting a new backup and—eventually either copying or re-initializing that weird TM and then restarting it then gives you one or hopefully two good backups. But it’s your data, and your budget.